Electroporation is the artificial means of DNA transfer into the cells using an electrical field. It is defined as the use of electrical field to reversibly form micropores in the cell membrane. It is relatively new, simple and rapid technique to introduce DNA in a wide variety of cells. This technique is based on the original observation of Zimmermann in 1983 that high current pulses can induce cell membranes to fuse.
Experiments have revealed that when subjected to electrical shock– brief exposure to a voltage gradient of 4000 to 8000 volts cm-1 – the cells takes DNA from the suspending medium through the momentarily created holes in the cell membrane. When the cells are exposed to an electric field, the components of the cell membrane become polarized and a potential difference develops across the membrane. When this potential difference exceeds the threshold level, the cell membrane breakdown in localized areas and the cell membrane becomes permeable to the exogenous DNA. The induced permeability is reversible if the electrical conditions are within the limit, otherwise irreversible changes occur in the cell membrane.
The technique of Electroporation requires the Electroporation instrument besides the cell culture and exogenous DNA sample. The Electroporation instrument consists of a Pulse generator, a chamber to suspend the cells between the electrodes, an oscilloscope to monitor the amplitude of the electric pulse etc. Generally 1.5Kv / cm is applied as electric pulse. Suitable temperature for Electroporation is 0 to 4 degree.
The Electroporation is carried out in sterile cuvettes and cells are suspended in osmotically buffered DNA solution contains salt. Electrodes are then placed in the cuvettes and electrical pulses are applied. These electrical pulses maybe high pulses of short duration (2500 volt for one milli second) or low pulses of long duration (200 volt for 50 milli second) depending on the experiment. If high pulses are applied, the electric discharge must be precisely controlled. When the current pulses make micropores in the cell membrane, exogenous DNA enters into the cell and the membrane reseals.
The electroporated cells are then transferred to fresh suspending medium and grown for two days. Transformation occurs during this period and about 25 to 30 transformants will be obtained per 105 live cells. Electroporation technique is not suitable for cells having cell wall. This is carried out in plant protoplasts, mammalian primary cell lines, yeast protoplasts, bacterial protoplasts etc.